Conventionally, there has been known a mobile communication system supporting a 2 G/3 G radio access network (UTRAN: Universal Terrestrial Radio Access Network or GERAN: GSM EDGE Radio Access Network), and an LTE (Long Term Evolution) scheme radio access network (E-UTRAN: Evolved Universal Terrestrial Radio Access Network).
The 3GPP TS23.216 specifies “SRVCC (Single Radio Voice Call Continuity) scheme” of switching a path for voice communications between a UE (User Equipment) #1 and a UE#2 from a path (a path for VoIP (Voice over IP) communications) via the E-TRAM or GERAN to a path (a path for circuit switch (CS: Circuit Switch) communications) via the UTRAN/GERAN (see, Non-patent document 1).
In addition, the Alt. 4, Alt. 10, Alt. 11, Alt. 12, etc., of the 3GPP TR23.856 v0.4.1 specify an SRVCC scheme (hereinafter, referred to as an SRVCC enhancement scheme) of switching a path for voice communications between UE#1 and UE#2 from a path via the E-UTRAN to a path via the UTRAN/GERAN in a visited network of the UE#1.
The SRVCC enhancement scheme can terminate signals required for switching a path for voice communications between the UE#1 and the UE#2 within the visited network of the UE#1. As compared with the conventional SRVCC scheme, a communication interruption time due to exchange of the signals between the visited network of the UE#1 and the home network of the UE#1 can be shortened.